The present invention is generally directed to rapid thermal processing chambers for heating semiconductor wafers using light energy. More particularly, the present invention is directed to rapid thermal processing chambers that are capable of processing a plurality of wafers at the same time.
Various heating devices have been proposed in the past for processing semiconductor wafers. These heating devices can be classified into two basic configurations. The first is a batch system in which multiple wafers (25 wafers to about 200 wafers) are loaded into a round tubular furnace and slowly heated to the desired temperature. Batch systems can be considered temperature equilibrium devices in that the furnace walls are approximately at the same temperature as the heating elements and the wafers being heated. Batch systems are typically referred to as xe2x80x9chot wallxe2x80x9d systems since the furnace walls are at an elevated temperature. The primary advantage of a batch system is the ability to process many wafers at the same time therefore reducing the processing cost per wafer. The disadvantage of such a configuration, however, is the speed in which the wafer temperature can be elevated or cooled. The large thermal mass of a batch furnace prevents quick temperature changes and forces relatively long process times, ranging from about fifteen minutes to about five hours.
A second and newer approach to wafer heating is rapid thermal processing where a single wafer is heated in a small compartment using radiant energy as the energy source. For instance, such systems typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafer is heated under controlled conditions according to a preset temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, rapid thermal processing chambers also typically include temperature sensing devices, such as pyrometers, that sense the radiation being emitted by a semiconductor wafer at a selected band or wavelength. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
In alternative embodiments, instead of or in addition to using radiation sensing devices, rapid thermal processing chambers can also contain thermocouples for monitoring the temperature of the wafers. Thermocouples measure the temperature of objects by direct contact.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical reactions can take place as the wafer is fabricated into a device. During rapid thermal processing, semiconductor wafers are typically heated by arrays of lights to temperatures, for instance, from about 400xc2x0 C. to about 1,200xc2x0 C., for times which are typically less than a few minutes and in most cases less than one minute.
Rapid thermal processing chambers typically operate in a non-equilibrium state. Specifically, the walls surrounding the wafer are kept cool, with active cooling, and thus are typically referred to as xe2x80x9ccold wallxe2x80x9d systems. The non-equilibrium configuration refers to the fact that the filament temperature inside the radiant source is at a much higher temperature than the wafer. The key advantage of using rapid thermal processing systems is the ability to quickly change wafer temperature therefore enabling very short heating cycles which can be between about one second to about two minutes. The drawback of rapid thermal processing systems, however, is the cost per wafer processed, especially for cycles between 60 and 120 seconds long, since the systems are only equipped to heat one wafer at a time.
In view of the above, a need currently exists for a thermal processing chamber that is capable of rapidly heat treating a plurality of wafers at the same time. Specifically, a need exists for a thermal processing chamber capable of accommodating a plurality of wafers as in a batch system, but yet also capable of processing the wafers very rapidly, such as in a rapid thermal processing system.
The present invention recognizes and addresses the foregoing disadvantages and others of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved thermal processing chamber for heat treating semiconductor wafers.
Another object of the present invention is to provide a thermal processing chamber that is capable of heat treating a plurality of wafers at the same time.
Still another object of the present invention is to provide a multiwafer thermal processing chamber that heats the wafers using light energy.
Another object of the present invention is to provide a multiwafer thermal processing system that rapidly processes a plurality of semiconductor wafers in a xe2x80x9ccold wallxe2x80x9d chamber.
These and other objects of the present invention are achieved by providing a multiwafer thermal processing system. The system includes a thermal processing chamber adapted to receive a plurality of stacked semiconductor wafers. A plurality of light energy sources are placed in communication with the thermal processing chamber for the heating semiconductor wafers contained in the chamber. Specifically, the plurality of light energy sources are positioned so as to encircle the thermal processing chamber. Light energy sources can also be placed at the top and at the bottom of the chamber if desired.
A substrate holder is contained within the thermal processing chamber. The substrate holder is configured to hold the plurality of semiconductor wafers. In particular, the wafers are held in a stacked arrangement wherein adjacent wafers are spaced a distance sufficient for light energy being emitted by the light energy sources to contact the entire bottom and top surfaces of the wafers.
In one embodiment, the system further includes at least one temperature sensing device for monitoring the temperature of the semiconductor wafers. For instance, the temperature sensing devices can be pyrometers, thermocouples or a combination of pyrometers and thermocouples. A controller, such as a microprocessor is placed in communication with the temperature sensing devices and the light energy sources. The controller is configured to control the amount of light energy being emitted by the light energy sources in response to temperature information received from the temperature sensing devices. In this manner, the wafers can be heated uniformly and according to a preset temperature regime.
The system of the present invention is capable of heating a plurality of semiconductor wafers (from 2 to 10 wafers) to a temperature range from 200xc2x0 C. to 1,200xc2x0 C. The system is capable of heating wafers to the above described temperatures in a very short period of time, such as from about one minute to about five minutes.
For most applications, the light energy sources should be positioned outside of the thermal processing chamber so the light energy sources do not contaminate wafers contained in the chamber. In one embodiment, the thermal processing chamber can include one or more windows designed to allow light energy being emitted by the light energy sources to pass into the chamber.
The light energy sources used in the system of the present invention can have various shapes and can be positioned around the thermal processing chamber at various locations and according to various patterns. In one embodiment, the light energy sources can comprise lamps having an elongated housing. The lamps can be positioned such that the elongated housing faces the thermal processing chamber. The lamps can be placed around the thermal processing chamber so that the elongated housing is parallel to a vertical axis of the chamber. Alternatively, the lamps can be placed perpendicular to the vertical axis of the chamber. Preferably, the system includes reflectors positioned behind the light energy sources. The reflectors can be used to direct light energy being emitted by the light energy sources into the thermal processing chamber.
In an alternative embodiment of the present invention, instead of the light energy sources directly heating the semiconductor wafers, the light energy sources can be used to heat a thermally conductive lining which in turn heats the wafers. For instance, the thermal processing system of the present invention can contain a lining that is positioned so as to surround semiconductor wafers held on the substrate holder in the thermal processing chamber. The lining can be in the shape of a cylindrical sleeve that can have a top and a bottom for completely enclosing the substrate holder and the wafers. The thermally conductive lining can be made from various materials including, for instance, silicon carbide.
In this embodiment, in order to monitor the temperature of the wafers during processing, one or more temperature sensing devices can be used to sense the temperature of the thermally conductive lining. The system can be calibrated such that the temperature of the wafers contained within the thermal processing chamber can be determined by knowing the temperature of the lining.
In a further alternative embodiment of the present invention, the multiwafer thermal processing system can include energy dispersing members located within the thermal processing chamber for distributing light energy being emitted by the light energy sources onto the semiconductor wafers. For instance, in one embodiment, the energy dispersing members can be in the shape of plates spaced in between semiconductor wafers held within the chamber. Light energy sources can be positioned to emit light energy directly into the energy dispersing members. The energy dispersing members can redirect the light energy onto the adjacent wafers.
The energy dispersing members can be made from various materials and can have any shape sufficient to refract and disperse light. In one embodiment, the energy dispersing members can be quartz plates containing areas having a different index of refraction than the quartz. For instance, the areas having a different index of refraction can be made from glass particles, such as glass spheres.
In an alternative embodiment, the energy dispersing members can be quartz plates having a shape that is designed to refract light. For instance, sharp angles can be formed into the quartz plate which cause light energy in the plate to be scattered in various directions. Preferably, light energy sources are positioned adjacent the side surfaces of each of the energy dispersing members. In this manner, light energy directly enters the dispersing members and is distributed to adjacent wafers. In order to maximize the amount of light energy that enters the light dispersing members, reflectors can also be placed around the light energy sources.
Other objects, features and aspects of the present invention are discussed in greater detail below.